Need to turn on laser for only 5 millisecs then off for 2 secs then on again!

Thread Starter

leimignej

Joined Apr 20, 2021
15
I recently began working on a project for school.

I need to create a circuit that turns a laser diode for 5 milliseconds then off. then wait 2-3 secs then on again. the time when off does not need to be so precise cold be between 2 seconds to 5 it does not matter for now.

I don't have lots of experience but do understand basic electronic concepts. I would like this project to be as simple as possible. without the use of specialized ics or even 555s. I have in mind something like an npn transistor to be used as a switch and capacitors as timers. using the time it takes to charge and discharge capacitors to my advantage. I don't know it it would be wise or even posible to use a relay instead of a transistor for those switching speeds.

I have the following materials at hand

* LDRs
* 650nm 3v 5mW laser diodes
* almost any size resistors
* almost any size capacitors and types
* 5vdc and 12vdc relays
* LD13003A NPN transistors (over 10 units)
* BUX80 NPN transistors (over 20 units)
* TIP32A PNP transistors (over 20 units)
* Prototype pcb boards
* lots of free time!
 

sagor

Joined Mar 10, 2019
479
I don't have a direct answer as to how to do it, but relays are "out". Most relays have around 8 to 20ms closing time, and have contact bounce. Not good for a 5ms timing event.
 

Thread Starter

leimignej

Joined Apr 20, 2021
15
I don't have a direct answer as to how to do it, but relays are "out". Most relays have around 8 to 20ms closing time, and have contact bounce. Not good for a 5ms timing event.
I imagined relays were not viable for this! relays are out of the question!
 

Yaakov

Joined Jan 27, 2019
3,523
They are cheap ones from amazon. "XINGYHENG Mini Laser Dot Diode Module Head WL Red 650nm 6mm 5mW 3V"
So there are modules with drivers then. What are you trying to accomplish? How accurate does the on time have to be?

If you can explain what it will be used for it will help a lot.
 

Thread Starter

leimignej

Joined Apr 20, 2021
15
So there are modules with drivers then. What are you trying to accomplish? How accurate does the on time have to be?

If you can explain what it will be used for it will help a lot.
Yes sure!! thanks a lot for your input by the way!!!


it is basically a loop! laser needs to be on for around 5ms then off for 2-5secs then repeat the process. the important timming event here that needs to be somewhat precise is the time the laser is on! then the resting time could vary to whatever. its is not critical
 

Yaakov

Joined Jan 27, 2019
3,523
Yes sure!! thanks a lot for your input by the way!!!


it is basically a loop! laser needs to be on for around 5ms then off for 2-5secs then repeat the process. the important timming event here that needs to be somewhat precise is the time the laser is on! then the resting time could vary to whatever. its is not critical
Those details I have understood but what will the laser be doing? What is "somewhat precise"? You are going to have a lot of trouble using RC timing to maintain accuracy.
 

Yaakov

Joined Jan 27, 2019
3,523
A point to consider: the laser modules you have include driver boards that will not be very happy about switching fast. They are designed to be constant current and I will be surprised if you get much output trying to power them for 5ms.
 

Thread Starter

leimignej

Joined Apr 20, 2021
15
Those details I have understood but what will the laser be doing? What is "somewhat precise"? You are going to have a lot of trouble using RC timing to maintain accuracy.

the laser cannot be on for more than 5ms because it would then be very noticeable to our eyes. at the receiving end of the laser beam there will be a photo transistor, ldr or something of similar function that can be activated with light and later decode the signal.

this project will be kind of an encripted laser messaging! if the tests go well i will later set up an arduino to encript a message and other one to decipher the message. there are similar devices in the market right now and some use infra red or ultra violet waves to achieve it. I just want to make a very simplistic version as a school proyect.

the lasers i am using are not very strong but I will make sure 100% everyone near this thing when it's on will be wearing laser safety googles that cover the 650nm red lasers!
 

BobTPH

Joined Jun 5, 2013
3,691
Why? I don't think there is anything in there except a raw diode and a lens. If that is correct, it should have not problem pulsing for 5ms.

Edit: replaying to Yaakov

Bob
 

BobTPH

Joined Jun 5, 2013
3,691
Okay. I was not aware of that. None of the ads for them say anything about that, some caution you that the operating current must be less then 20ma, so, I am still skeptical.

Bob
 

Yaakov

Joined Jan 27, 2019
3,523
I was dumb enought and already bought them. I thought it would be easier than making the driver myself! is it too complicated to make a suitable laser diode driver myself?
The driver isn't complex. It has to provide a constant current to avoid frying the diode. A 5ms pulse might not require a driver because it won't get the diode hot enough to hurt it.

You will still need to do two very difficult things: time 5ms with an RC circuit and time 5 seconds with an RC circuit.
 

Thread Starter

leimignej

Joined Apr 20, 2021
15
Okay. I was not aware of that. None of the ads for them say anything about that, some caution you that the operating current must be less then 20ma, so, I am still skeptical.

Bob
so it is 100% out of the question to use the original driver that came with them?
 

Yaakov

Joined Jan 27, 2019
3,523
Okay. I was not aware of that. None of the ads for them say anything about that, some caution you that the operating current must be less then 20ma, so, I am still skeptical.

Bob
They mass produce theses things for use in laser pointers, the little driver boards are pretty standard. The current limits are for the diode, to be sure, but the voltage applied can be between 3 and 5V for the same module with no other components.
 

Thread Starter

leimignej

Joined Apr 20, 2021
15
The driver isn't complex. It has to provide a constant current to avoid frying the diode. A 5ms pulse might not require a driver because it won't get the diode hot enough to hurt it.

You will still need to do two very difficult things: time 5ms with an RC circuit and time 5 seconds with an RC circuit.

What would be your aproach to this issue? what ics would you use for the timming?
 

Yaakov

Joined Jan 27, 2019
3,523
Okay. I was not aware of that. None of the ads for them say anything about that, some caution you that the operating current must be less then 20ma, so, I am still skeptical.

Bob
Let's just say I have never seen a raw diode sold as a "module" and these do not seem to be an exception. It's not impossible but I wouldn't bet much on these being different, they are bg standard in appearance.
 
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